1. Field of the Invention
The present invention relates to a wire electrode which is employed for wire electro-discharge machining, and to a method of manufacturing method thereof.
2. Description of the Background Art
Wire electro-discharge machining is a method of causing intermittent discharge between a linear working electrode called a wire electrode for electro-discharge machining and a workpiece through a working fluid such as water or oil. The workpiece is moved relative to the wire electrode for electro-discharge machining, thereby melting and cutting the workpiece into a desired configuration. This method is utilized for manufacturing various types of metal molds and the like. In such wire electro-discharge machining, required are processing characteristics such as excellent finishing, high working accuracy, good finished surface state of the workpiece, no adhesion of the wire electrode material to the workpiece, and a short electro-discharge machining time. A wire electrode employed for such wire electro-discharge machining is generally prepared from a brass wire, which has good drawability and high strength required for a wire electrode.
As working power sources have been improved/advanced, it is desirable to provide a wire electrode which can improve processing speed. A wire electrode for improved processing speed is particularly desired for applications employing a power source of a wire electro-discharge machining which repeatedly applies a high and short-time pulse voltage.
However, wire electrodes for electro-discharge machining typically prepared from a brass wire are incapable of attaining a sufficiently high processing speed. Further, brass wires are problematic in that electrode material adheres to the workpiece. As a result, the cut surface of the workpiece is roughened and the wire electrode is easily broken when electro-discharge machining is performed at a high processing speed.
A wire electrode for wire electro-discharge machining prepared by covering a core formed of Cu (copper) or a Cu alloy with Zn (zinc), or prepared by covering the core with Zn, heat treating to generate a Cu--Zn alloy at a surface layer by diffusion and having an oxide film on the outermost surface has been used in some applications. The Zn coated Cu or Cu alloy wire electrode results in improved cut surface of the workpiece; however, it cannot provide a sufficiently high processing speed. The diffusion alloy coated wire electrode improves to some extent the processing speed; however, the property of the cut surface of the workpiece is not sufficiently improved and it is difficult to position the wire electrode before starting electro-discharge machining. As compared with the brass wire, the conventional wire electrode for wire electro-discharge machining having a core and a coating layer formed on an outer periphery of the core has improved electro-discharge machining characteristics. However, the wire electrode itself, a wire contact (a roller or die for feeding electricity), a guide die and the like suffer wear and undergo considerable damage, thereby shortening their lifetime and significantly increasing the cost of electro-discharge machining.